1. Field of the Invention
The present invention relates to a piston for a cartridge having a cylinder-like or cylindrical tube-like base member which can be inserted into a cartridge and is displaceable along the cylindrical longitudinal axis in a cartridge and a corresponding cartridge for holding and storing liquid, powder or paste-like compounds and a system comprising a corresponding cartridge and a tool for displacing the piston in the cartridge.
2. Prior Art
Cartridges for holding liquid, paste-like or powder compounds have long been known for all kinds of engineering applications. A distinction is made between cartridges, which have only a single chamber for a corresponding compound or several chambers for storing different components separately and mixing them during processing. Examples of this are two-component adhesives, in which the components are stored separately and are mixed together during application in order that corresponding curing processes may be initiated.
Such cartridges have different designs, such as so-called side-by-side forms in which the chambers are beside each other, and coaxial cartridges in which the chambers are arranged coaxially inside each other.
These various cartridges, which can be used for all kinds of purposes, share the fact that usually one or more pistons are provided, which are accordingly displaceably accommodated in the chambers, such that the compounds held in the chambers can be discharged through a dispensing opening by means of the pistons. Apart from filling of the chambers via the dispensing openings, filling is usually effected via the piston-side open end of the corresponding chamber. Accordingly, when a cartridge is filled, the compound is introduced into it at the piston-side open end of the chamber, whereafter the open end is then sealed with the piston. The piston must be held tightly against the walls of the chamber to prevent the liquid, paste-like or powder-like compound from leaving the chamber. The problem with this, however, is that, during filling and initial insertion of the piston, care must be taken to allow air in the chamber to escape as the piston is being brought into contact with the compound held in the chamber.
To this end, various solutions are known such as are described in the prior art, e.g. in German Utility Model DE 295 06 800, European Patent Application EP 1 738 834 A1, European Patent Application EP 1 514 812 A1, European Patent EP 0 497 739 B1, European Patent Application EP 344 491 A1, European Patent Application EP 463 991 A1, U.S. Pat. No. 6,899,254 B1, PCT application WO 03/050012 A1, PCT application WO 01/94028.
In these publications, various pistons with ventilation devices are disclosed which describe inter alia pistons, that can have different valves which are usually in the central area of the piston and which are open during the closing process in order to allow air to escape and which, after the chamber opening has been closed with the piston, can themselves be closed to prevent the compound held in the chamber from escaping.
The disadvantage of this prior-art solution, however, is that the pistons become very complex owing to the configuration of the valves and thus are very complicated to produce. Moreover, such valves are prone to malfunction and leaks can occur when they are actuated again. In addition, the closing process itself can be complicated if, apart from setting of the piston, a second operation to close the valve or valves becomes necessary. An additional disadvantage is that, when the chamber is closed by means of the piston, the compound held therein can assume a conical shape which has the effect that, in the central area, where the valves are usually arranged, the compound held in the chamber impinges first on the piston and thus complete venting is no longer possible.
Moreover, the above-mentioned prior art discloses cover plates which prevent the actual piston member from making direct contact with potentially chemically reactive compounds. In accordance with the above-cited prior art, such cover plates can be integrated into appropriate ventilation devices.